Monday, June 4, 2012

'THE first time I questioned the conventional wisdom on the nature of a healthy diet, I was in my salad days, almost 40 years ago, and the subject was salt. Researchers were claiming that salt supplementation was unnecessary after strenuous exercise, and this advice was being passed on by health reporters. All I knew was that I had played high school football in suburban Maryland, sweating profusely through double sessions in the swamplike 90-degree days of August. Without salt pills, I couldn't make it through a two-hour practice; I couldn't walk across the parking lot afterward without cramping.

While sports nutritionists have since come around to recommend that we should indeed replenish salt when we sweat it out in physical activity, the message that we should avoid salt at all other times remains strong. Salt consumption is said to raise blood pressure, cause hypertension and increase the risk of premature death. This is why the Department of Agriculture's dietary guidelines still consider salt Public Enemy No. 1, coming before fats, sugars and alcohol. It's why the director of the Centers for Disease Control and Prevention has suggested that reducing salt consumption is as critical to long-term health as quitting cigarettes.

And yet, this eat-less-salt argument has been surprisingly controversial — and difficult to defend. Not because the food industry opposes it, but because the actual evidence to support it has always been so weak.

When I spent the better part of a year researching the state of the salt science back in 1998 — already a quarter century into the eat-less-salt recommendations — journal editors and public health administrators were still remarkably candid in their assessment of how flimsy the evidence was implicating salt as the cause of hypertension.

"You can say without any shadow of a doubt," as I was told then by Drummond Rennie, an editor for The Journal of the American Medical Association, that the authorities pushing the eat-less-salt message had "made a commitment to salt education that goes way beyond the scientific facts."

While, back then, the evidence merely failed to demonstrate that salt was harmful, the evidence from studies published over the past two years actually suggests that restricting how much salt we eat can increase our likelihood of dying prematurely. Put simply, the possibility has been raised that if we were to eat as little salt as the U.S.D.A. and the C.D.C. recommend, we'd be harming rather than helping ourselves.

WHY have we been told that salt is so deadly? Well, the advice has always sounded reasonable. It has what nutritionists like to call "biological plausibility." Eat more salt and your body retains water to maintain a stable concentration of sodium in your blood. This is why eating salty food tends to make us thirsty: we drink more; we retain water. The result can be a temporary increase in blood pressure, which will persist until our kidneys eliminate both salt and water.'